The present invention relates to the field of fuel injection systems for internal combustion engines in which the injected fuel is supplied to the intake system of the engine via a fuel injector or injectors, and in particular relates to the field of such fuel injection systems in which the pressure of the fuel supplied to the fuel injector or injectors is controlled by a pressure regulator valve of the so called open to atmosphere type.
The present patent application has been at least partially prepared from material which has been included in Japanese Patent Applications Nos. Sho 60-020729 (1985) and Sho 60-049553 (1985), which were invented by the same inventors as the present patent application, and the present patent application hereby incorporates the text of those Japanese Patent Applications and the claims and the drawings thereof into this specification by reference; copies are appended to this specification.
In a conventional such type of fuel injection system for an internal combustion engine such as an automobile engine, such as the so called D jetronic fuel injection system, liquid fuel (i.e. gasoline) is pumped up from a fuel tank and is pressurized by a fuel pump, being then supplied to one or more fuel injectors fitted to the intake system of the engine. A control device opens and closes this injector (hereinafter in this specification the question of possibly plural injectors will be disregarded) with a certain timing, and thereby fuel is supplied into said intake system for the engine, to be sucked into the cylinders and combusted. The control system for this fuel injection system controls the amount of supplied fuel by varying the length of the time interval between the opening of the fuel injection valve and the closing thereof.
The amount of fuel supplied in one fuel injection spurt through the fuel injector can only be satisfactorily controlled by varying the length of the time interval between the opening of the fuel injection valve and the closing thereof, if the rate of flow of fuel through the fuel injector when it is open is substantially constant. Now, this rate of flow is substantially determined, in terms of a constant and unaltered construction for the fuel injector, by the pressure gradient thereacross, in other words by the difference between the absolute pressure value at which is maintained the fuel which is being fed to the fuel injector, and the absolute pressure value which is maintained within the intake system of the engine, near the nozzle of the fuel injector. Thus, provided that this pressure gradient across the fuel injector can be kept substantially constant, the amount of fuel supplied in one fuel injection spurt through the fuel injector is substantially proportional to the time interval that said fuel injector is open. Now, the pressure at which the fuel which is being fed to the fuel injector is maintained, which of course primarily is produced by the pressure due to atmospheric pressure plus the pressure due to the pumping effect of the fuel pump, is typically controlled by a pressure control valve. Therefore, in the prior art, in order to maintain the above described pressure gradient as constant, the pressure in the intake system of the engine has been supplied as a so called background or comparison pressure value to the pressure control valve for the supplied fuel. This pressure control valve has a valve so that it causes a certain determinate pressure value differential to be maintained between said absolute pressure value at which the fuel is being fed to the fuel injector is maintained, and said background absolute pressure value equal to the pressure in the intake system of the engine. This arrangement causes the value of the intake system pressure to be canceled out for determining the pressure gradient across the fuel injector, and also means that the current value of atmospheric pressure is irrelevant to said pressure gradient.
Thus, it is generally the case that: ##EQU1## where: V is the flow rate;
C is the areal coefficient; PA1 g is the acceleration of gravity; PA1 gamma (.gamma.) is the relative density of the fuel; PA1 Pf is the absolute pressure at the fuel injector; and PA1 Pm is the absolute intake manifold pressure.
Now, if the setting of the pressure control valve for the supplied fuel is equal to Ppr, then Pf=Pm+Ppr, and this reduces to: ##EQU2## and the flow rate through the fuel injector is of course not affected by the current value of the pressure in the intake system or by the current value of atmospheric pressure.
Now, this method and structure are in themselves satisfactory for ensuring that the flow rate through the fuel injector is constant, and accordingly for ensuring that the amount of fuel supplied in one fuel injection spurt through the fuel injector is substantially proportional to the time interval that said fuel injector is open. But, in order to supply the pressure in the intake system of the engine as a background pressure value to the pressure control valve for the supplied fuel, a conduit assembly is needed to conduct said pressure, and connections and fitting for this conduit assembly are required, which is troublesome during manufacture and assembly of the system. Particularly, a takeout port from the engine intake system to supply the pressure therein to the conduit system, such as for example from a surge tank incorporated in said intake system, is required. Further, the positioning of the pressure control valve is restricted by the requirement that it be connected to the conduit system, which is nuisance and leads to design inconvenience.
Another problem that can occur with a conventional fuel injection system in which the pressure of the fuel supplied to the fuel injector is regulated by a pressure regulator valve which is supplied with the pressure in the intake system of the engine as a so called background or comparison pressure value, is that, if said pressure in the intake system drops when the engine is idling, then the fuel pressure correspondingly drops, and this can cause fuel vapor to be introduced into the passages of the system, which can cause vapor lock and rough idling and so on.